Stellar model tests and age determination for RGB stars from the APO-K2 catalogue
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| Format: | Preprint |
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2024
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| author | Valle, G. Dell'Omodarme, M. Moroni, P. G. Prada Degl'Innocenti, S. |
| author_facet | Valle, G. Dell'Omodarme, M. Moroni, P. G. Prada Degl'Innocenti, S. |
| contents | By adopting the recently empirically derived dependence of $α$-elements on $[α/{\rm Fe}]$ instead of the conventionally applied uniform one, we tested the agreement between stellar model predictions and observations for red giant branch (RGB) stars in the APO-K2 catalogue. We particularly focused on the biases in effective temperature scales and on the robustness of age estimations. We computed a grid of stellar models relying on the empirical scaling of $α$-elements, investigating the offset in effective temperature $ΔT$ between these models and observations, using univariate analyses for both metallicity [Fe/H] and $[α/{\rm Fe}]$. To account for potential confounding factors, we then employed a multivariate generalised additive model to study the dependence of $ΔT$ on [Fe/H], $[α/{\rm Fe}]$, $\log g$, and stellar mass. The initial analysis revealed a negligible trend of $ΔT$ with [Fe/H], in contrast with previous works in the literature. A slight $ΔT$ difference of 25 K was detected between stars with high and low $α$-enhancement. Our multivariate analysis reveals a dependence of $ΔT$ on both [Fe/H] and $[α/{\rm Fe}]$, and highlights a significant dependence on stellar mass. This suggests a discrepancy in how effective temperature scales with stellar mass in the models compared to observations. Despite differences in assumed chemical composition, our analysis, through a fortunate cancellation effect, yields ages that are largely consistent with recent studies of the same sample. Notably, our analysis identifies a 6% fraction of stars younger than 4 Ga within the high-$α$ population. However, our analysis of the [C/N] ratio supports the possible origin of the these stars as a result of mergers or mass transfer events. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2408_14900 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Stellar model tests and age determination for RGB stars from the APO-K2 catalogue Valle, G. Dell'Omodarme, M. Moroni, P. G. Prada Degl'Innocenti, S. Solar and Stellar Astrophysics Astrophysics of Galaxies By adopting the recently empirically derived dependence of $α$-elements on $[α/{\rm Fe}]$ instead of the conventionally applied uniform one, we tested the agreement between stellar model predictions and observations for red giant branch (RGB) stars in the APO-K2 catalogue. We particularly focused on the biases in effective temperature scales and on the robustness of age estimations. We computed a grid of stellar models relying on the empirical scaling of $α$-elements, investigating the offset in effective temperature $ΔT$ between these models and observations, using univariate analyses for both metallicity [Fe/H] and $[α/{\rm Fe}]$. To account for potential confounding factors, we then employed a multivariate generalised additive model to study the dependence of $ΔT$ on [Fe/H], $[α/{\rm Fe}]$, $\log g$, and stellar mass. The initial analysis revealed a negligible trend of $ΔT$ with [Fe/H], in contrast with previous works in the literature. A slight $ΔT$ difference of 25 K was detected between stars with high and low $α$-enhancement. Our multivariate analysis reveals a dependence of $ΔT$ on both [Fe/H] and $[α/{\rm Fe}]$, and highlights a significant dependence on stellar mass. This suggests a discrepancy in how effective temperature scales with stellar mass in the models compared to observations. Despite differences in assumed chemical composition, our analysis, through a fortunate cancellation effect, yields ages that are largely consistent with recent studies of the same sample. Notably, our analysis identifies a 6% fraction of stars younger than 4 Ga within the high-$α$ population. However, our analysis of the [C/N] ratio supports the possible origin of the these stars as a result of mergers or mass transfer events. |
| title | Stellar model tests and age determination for RGB stars from the APO-K2 catalogue |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2408.14900 |